In order to provide improved communication services and increased efficiency, cellular communication systems are continuously developed and enhanced. Currently, the 3rd Generation Partnership Project (3GPP) standards body is in the process of standardising improvements to the Universal Mobile Telecommunication System (UMTS) known as Long Term Evolution (LTE).
Similarly, to advanced communication services, such as High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), LTE uses very fast scheduling of communication resources allocated to user traffic and control data over the air interface. Specifically, scheduling for user traffic may be performed in the individual serving base station (node B) thereby allowing scheduling to be so fast that it can follow changes in the characteristics of the propagation channels to the individual User Equipments (UEs). This is used to schedule data for UEs such that data is predominantly scheduled for UEs which currently experience advantageous propagation conditions. The fast scheduling may be performed both for uplink user data traffic transmitted on a physical channel known as the Physical Uplink Shared CHannel (PUSCH) and for downlink user data traffic transmitted on a physical channel known as the Physical Downlink Shared CHannel (PDSCH).
In LTE, the resource allocation can be changed in subframes having a duration of only 1 msec with a typical scheduling interval (i.e. how often the scheduling algorithm runs) of between 1 and 10 sub-frames. One frame consists of 10 such consecutive subframes. The PUSCH and PDSCH are shared channels wherein the scheduling is not only dependent on the current propagation conditions but also on the resource requirement of the UEs. In order to simplify the scheduling and to reduce the signalling overhead, LTE allows for persistent scheduling wherein a resource allocation for the PUSCH or PDSCH may be made for a plurality of frames.
In order to provide efficient fast scheduling in the base station, the UE must transmit uplink control information to the scheduling base station. Specifically, the UE transmits Channel Quality Indicator (CQI) data which is indicative of the current propagation conditions for the UE. Based on measurements of the received signal the UE generates a CQI which may indicate a modulation scheme and data rate that is considered to be supportable by the air interface communication channel from the base station to the UE, or which may be a measure of the Signal to Noise plus Interference Ratio. As another example, LTE uses a retransmission scheme (referred to as ARQ or Hybrid ARQ (HARQ)) and the UE transmits ARQ data in the form of uplink acknowledge (ACK) or non-acknowledge (NACK) messages which are used to determine whether individual data packets need to be retransmitted. As yet another example, LTE allows the base station to utilise adaptive antenna technology and the UE may report Precoding Matrix Index (PMI) which is used to signal the antenna weights recommended by the UE for the individual antenna elements.
The uplink control information is transmitted using physical uplink channels. Specifically, in subframes wherein the UE transmits uplink user data traffic on the PUSCH, the control data is embedded within the transmission such that the control information is transmitted to the base station using the PUSCH. However, for subframes wherein no uplink user data traffic is transmitted on the PUSCH, the UE uses a physical uplink channel known as the Physical Uplink Control CHannel (PUCCH) to transmit the control information. Thus, the physical air interface channel used for the transmission of the control information may change for different subframes.
Although this approach has some advantages it tends to also have some disadvantages and tends to be inefficient. For example, the resource of the PUCCH tends to be limited and may in some cases limit the capacity of the system as a whole. Also, as the control information may be transmitted on different physical uplink air interface channels, the base station typically needs to decode both of these channels in order to determine on which channel the data was transmitted.
Hence, an improved 3GPP system would be advantageous and in particular a system allowing increased flexibility, improved resource utilisation, facilitated operation and/or improved performance would be advantageous.